High-Resolution Secondary Ion Mass Spectrometry Reveals the Contrasting Subcellular Distribution of Arsenic and Silicon in Rice Roots      

Abstract

Rice (Oryza sativa) takes up arsenite mainly through the silicic acid transport pathway. Understanding the uptake and sequestration of arsenic (As) into the rice plant is important for developing strategies to reduce As concentration in rice grain. In this study, the cellular and subcellular distributions of As and silicon (Si) in rice roots were investigated using high-pressure freezing, high-resolution secondary ion mass spectrometry, and transmission electron microscopy. Rice plants, both the lsi2 mutant lacking the Si/arsenite efflux transporter Lsi2 and its wild-type cultivar, with or without an iron plaque, were treated with arsenate or arsenite. The formation of iron plaque on the root surface resulted in strong accumulation of As and phosphorous on the epidermis. The lsi2 mutant showed stronger As accumulation in the endodermal vacuoles, where the Lsi2 transporter is located in the plasma membranes, than the wild-type line. As also accumulated in the vacuoles of some xylem parenchyma cells and in some pericycle cells, particularly in the wild-type mature root zone. Vacuolar accumulation of As is associated with sulfur, suggesting that As may be stored as arsenite-phytochelatin complexes. Si was localized in the cell walls of the endodermal cells with little apparent effect of the Lsi2 mutation on its distribution. This study reveals the vacuolar sequestration of As in rice roots and contrasting patterns of As and Si subcellular localization, despite both being transported across the plasma membranes by the same transporters.

Silicon induced Fe deficiency affects Fe, Mn, Cu and Zn distribution in rice (Oryza sativa L.) growth in calcareous conditions

“…3G, Table 2 authors also showed that Fe plaque is composed of fine needles approximately10 nm 344 thick and 200 to 300 nm long, and this is why the Fe plaque does not appear as a sharp 345 line in the nanoSIMS images (Moore et al, 2011). This fact was also evident in our 346 study (Fig.3G), in which, using SEM-EDX analysis, a discontinuous Fe accumulation 347 was detected along the root surface.…”

“…The large majority of the available information related to the localization of 92 Fe, Mn, Cu, Zn and Si in rice is focused on rice seeds using S-XRF (Lu et al, 2013). Moore et al, 2011). 103 6 mL HNO 3 (65%), 2 mL H 2 O 2 (30%), and 1 mL HF (40%), using a microwave (CEM 135…”

Examination of the Distribution of Arsenic in Hydrated and Fresh Cowpea Roots Using Two- and Three-Dimensional Techniques

“…Although the subcellular distribution of As was not examined in this study, the data suggest a role of the endodermis (and border cells) in limiting this movement of As from the roots to the shoots. These observations are somewhat similar to those reported for rice roots examined using nano-secondary ion mass spectrometry (Moore et al, 2011), in which the highest concentrations of As were in the endodermis, pericycle, and xylem parenchyma cells, with little accumulation in the cortex and rhizodermis. For rice, the accumulation of As may also occur at the exodermis (the outermost layer of the cortex), which serves as an apoplastic barrier (Hose et al, 2001;Zhao et al, 2009Zhao et al, , 2010.…”

“…A limited number of studies have investigated As distribution in roots. For instance, Moore et al (2011) used nano-secondary ion mass spectrometry to investigate As distribution with subcellular resolution in cryosubstituted roots of rice. Hansel et al (2001) examined freeze-dried roots of Phalaris arundinacea (an aquatic species).…”

New highlights of phytolith structure and occluded carbon location: 3-D X-ray microscopy and NanoSIMS results

“…A micrometric proteinaceous scaffold, which averaged 2 % C dry weight, could be detected in the siliceous structure (Müller et al, 2010). The NanoSIMS technique was also used for identifying silicification sites in rice roots (Moore et al, 2011 C] − ratio were also created. Line scans were drawn across the analyzed surfaces and ion intensity vs. distance along the line were plotted.…”